
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21745.43    171.3695    22527.76    21409.52    22081.33
experime |  17,281    21902.82    174.8668    22987.51    21560.06    22245.57
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -157.3895    244.8385                -637.281     322.502
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    diff = mean(control) - mean(experime)                         t =  -0.6428
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2602         Pr(|T| > |t|) = 0.5203          Pr(T > t) = 0.7398
